1. Field of the Invention
The present invention relates to a solid state imaging device and a method for driving the same.
2. Description of the Related Art
As a CCD solid state imaging device, there has been known a CCD solid state imaging device of, for example, a frame interline transfer (FIT) system, a multiple-frame interline transfer (M-FIT) system and so on.
As shown in FIG. 1, a CCD solid state imaging device 1 of the frame interline transfer (FIT) system is formed of an imaging section 4 which comprises a plurality of light receiving portions 2, each serving as a pixel, arranged in a matrix fashion and vertical transfer registers 3 of a CCD structure each corresponding to each column of the light receiving portions 2, a storage section 6 comprising vertical transfer registers 5 of a similar CCD structure corresponding to the respective vertical transfer registers 3 in the imaging section 4, a horizontal transfer register 7 adjacent to the storage section 6, and an output section 8.
In the CCD solid state imaging device 1, a signal charge obtained by photoelectric-converting a light in the light receiving portion 2 is read to the vertical transfer register 3 and then once transferred at a high speed (so-called high speed frame shift) to the vertical transfer register 5 in the storage section 6. Thereafter, the signal charge at every one horizontal line is transferred from the storage section 6 to the horizontal transfer register 7, transferred within the horizontal transfer register 7 and outputted as a signal from the output section 8 sequentially.
In the CCD solid state imaging device 1 of the FIT system, since a period within which the signal charge resides in the vertical transfer register 3 in the imaging section 4 to which a light may be leaked can be shortened by the frame shift, a smear component charge can be reduced.
As shown in FIG. 2, a CCD solid state imaging device 11 of a multiple frame interline transfer (M-FIT) is formed of an imaging section 14 comprising a plurality of light receiving portions 12, each serving as a pixel, arranged in a matrix fashion and vertical transfer registers 13 of a CCD structure corresponding to columns of the light receiving portions 12, respectively, a storage section 16 having vertical transfer registers of the CCD structure made of transfer portions with a stage number twice as that of, for example, the vertical transfer registers 13 in the imaging section 14 in correspondence with the vertical transfer register 13, that is, a first storage section 16A having vertical transfer registers 15A made of transfer portions same as the vertical transfer registers 13 in half the stage number and a second storage section 16B contiguous to the first storage section 16A and having vertical transfer registers 15B made of transfer portions same as the former in half the stage number, a horizontal transfer register 17 contiguous to the second storage section 16B, and an output section 18.
In the CCD solid state imaging device 11, within the same vertical blanking period, a signal charge of the light receiving portion 12 on an odd line is transferred first, and then a signal charge of the light receiving portion 12 on an even line is transferred, whereby all the signal charges are transferred.
Specifically, as shown in FIG. 2, the signal charge of the light receiving portion 12 on the odd line is read to the vertical transfer register 13, and then transferred to the vertical transfer register 15A of the first storage section 16A at a high speed transfer (high speed frame shift). Next, the signal charge of the light receiving portion 12 on the even line is read to the vertical transfer register 13, and then transferred to the vertical transfer register 15A of the first storage section 16A at a high speed transfer (high speed frame shift) and at the same time, the signal charge of the odd line stored in the first storage section 16A is transferred to the vertical transfer register 15B in the second storage section 16B at a high speed transfer (high speed frame shift).
Thereafter, the signal charge on every one horizontal line is transferred from the storage section 16 (16A, 16B) to the horizontal transfer register 17, transferred within the horizontal transfer register 17 and sequentially outputted from the output section 18 as a signal.
Then, the signals of all the pixels, that is, the signal on the odd line and the signal on the even line, which are separated and outputted, are rearranged in the original order after they are output from the output section 18.
According to the CCD solid state imaging device 11 of the M-FIT system, the sensitivity is improved as well as the smear is reduced.
In the CCD solid state imaging device 1 of the FIT system, as described above, the residing period of the signal charge in the vertical transfer register 3 of the imaging section 4 is shortened by the frame shift and then the smear is reduced. However, the smear component charge is generated during the frame shift and hence it is desireable to further reduce the smear. The generation of the smear component charge during the frame shift is directly proportional to the number of pixels in the vertical direction. A large number of vertical pixels may be found in devices such as a high definition television (HDTV).
Recently, although the smear in the CCD solid state imaging device used in a HDTV camera is reduced much, if this smear reduction is compared with that of the CCD solid state imaging device used in a camera for the conventional broadcasting (NTSC), it is still deteriorated by about one digit.
In order that the CCD solid state imaging device is used in both the HDTV camera and one conventional broadcasting camera commonly, the smear is required to be reduced by about one digit as compared with the present smear value.
In view of the above point, an object of the present invention is to propose a CCD solid state imaging device and its driving method which can reduce smear.
Another object of the present invention is to propose a CCD solid state imaging device which can be applied, in addition to a low smear reading, to a field reading and to an all pixel reading (frame reading) by the M-FIT system and also can be used in a HDTV camera, a conventional broadcasting camera and a movie camera in common.
A CCD solid state imaging device according to the present invention comprises an imaging section formed of a plurality of light receiving portions and vertical transfer registers, first and second storage sections capable of storaging the charge from the imaging section, a horizontal transfer register, and a smear drain region, in which one bit amount of a transfer portion in the vertical transfer register corresponds to two adjacent light receiving portions and the vertical transfer register has a charge storage capacity capable of transferring handling charge amounts of two pixels.
According to the above CCD solid state imaging device, since there are provided the first and second storage sections, the two light receiving portions correspond to one bit amount of the transfer portion in the vertical transfer register of the imaging section, and the vertical transfer register is capable of transferring the handing charge amount of two pixels, a smear component in an interlace mode can be reduced considerably and a so-called low smear reading is made possible.
In other words, after a first smear component charge in the vertical transfer register, which is generated in a light receiving and storage period, is swept away at a high speed, without reading a signal, a signal charge is high-speed transferred (so-called high speed frame shift) first, and a second smear component charge generated during the high speed transfer is finally stored in the second storage section. Then, if the signal charge is read out and then transferred at a high speed (so-called high speed frame shift), and an added charge in which the signal charge and the second smear component charge generated during the high speed transfer are added, is stored in the first storage section, by obtaining a difference between the signal of the second smear component charge and the signal of added charge in the outside, it is possible to produce an image signal in which the smear component is reduced remarkably.
According to the CCD solid state imaging device with the above arrangement, since the vertical transfer register can transfer the handling charge amount of two pixels, it becomes possible that the signal charge in the light receiving portion is read to the vertical transfer register and the signal charges of two pixels are mixed in the vertical transfer register. Then, if the mixed signal charge of two pixels is transferred at a high speed to the second storage section passing through the first storage section, a normal field read-out can be carried out.
Furthermore, since the CCD solid state imaging device with the above arrangement comprises the first and second storage sections, the CCD solid state imaging device can be applied to a frame reading, i,e., a reading of all pixels of the M-FIT system.
A driving method of a CCD solid state imaging device according to the present invention uses a CCD solid state imaging device formed of an imaging section having a light receiving portion and a vertical transfer register, first and second storage sections, a horizontal transfer register and a smear drain region, and carries out such a process that after a first smear component charge in the vertical transfer register is swept away, a signal charge is transferred at a high speed without being read, a second smear component charge generated during the high speed transfer is stored in the first storage section, then the signal charge is read to the vertical transfer register and transferred at a high speed, an added charge in which the second smear component charge generated during the high speed transfer and the signal charge are added, is stored in the first storage section and at the same time, the second smear component charge in the first storage section is transferred to the second storage section and stored therein, and a difference between the signal of the second smear component charge and the signal of the added charge is outputted in the outside.
According to the above driving method, after the first smear component charge generated in the vertical transfer register during the light receiving and storage period is swept away, the signal charge is transferred at a high speed without being read, then the signal charge is read and transferred at a high speed, an added charge of the signal charge and the second smear component charge is stored in the first storage section, only the second smear component charge is stored in the second storage section, and the difference between the corresponding signals is outputted in the outside, whereby the second smear component generated during the high speed transfer period is canceled out and hence the smear component can be reduced remarkably.
The CCD solid state imaging device according to the present invention comprises an imaging section formed of a plurality of light receiving portions, each serving as a pixel, and vertical transfer registers corresponding to respective columns of light receiving portions, first and second storage sections capable of storaging the charge from the imaging section, a horizontal transfer register, and a smear drain region, in which one bit amount of a transfer portion in the vertical transfer register corresponds to two adjacent light receiving portions, and the vertical transfer register has a charge storage capacity capable of transferring handling charge amounts of two pixels.
According to the present invention, in the above CCD solid state imaging device, there are provided a means for transferring, at a high speed, the signal charge of the light receiving portion without being read to the vertical transfer register and finally storing the smear component charge generated during the high speed transfer in the second storage section, a means for reading the signal charge of the light receiving portion to the vertical transfer register, transferring the same at a high speed and storing an added charge of the smear component charge generated during the high speed transfer and the signal charge in the first storage section, and a means for outputting a difference between the signal of the smear component charge and the signal of the added charge at the outside.
According to the present invention, in the above CCD solid state imaging device, there are provided a means for reading the signal charge of the light receiving portion to the vertical transfer register, mixing signal charges of ones of adjacent two light receiving portions in the vertical transfer register, transferring the same at a high speed to the second storage section and outputting the same as a signal in an odd field, and a means for reading the signal charge of the light receiving portion to the vertical transfer register, mixing signal charges of the other ones of adjacent two light receiving portions in the vertical transfer register, transferring the same at a high speed to the second storage section and outputting the same as a signal in an even field.
A driving method of a CCD solid state imaging device according to the present invention uses a CCD solid state imaging device formed of an imaging section having a plurality of light receiving portions, each serving as a pixel, and a vertical transfer register corresponding to each column of the light receiving portions, first and second storage sections capable of storing a charge from the imaging section, a horizontal transfer register and a smear drain region, and carries out such a process that after a first smear component charge in the vertical transfer register is swept away, a signal charge is transferred at a high speed without being read to the vertical transfer register, a second smear component charge generated during the high speed transfer is stored in the first storage section, then the signal charge of the light receiving portion is read to the vertical transfer register and transferred at a high speed, an added charge, in which the second smear component charge generated during the high speed transfer and the signal charge are added, is stored in the first storage section and at the same time, the second smear component charge in the first storage section is transferred to the second storage section and stored therein, and a difference between the signal of the second smear component charge and the signal of the added charge is outputted in the outside.